1. Field of the Invention
This invention relates to systems for the detection of explosives and other controlled substances such as drugs or narcotics. More particularly, the present invention relates to an integrated system consisting of a sampling chamber, a detection system, and a data processing system, for the detection of the vapor and/or particulate emissions of explosives and controlled substances in a non-invasive
2. Discussion of the Prior Art
In recent years there has been a steady increase in the illegal use of explosives as well as an increase in the transportation of contraband substances such as drugs or narcotics. It is impossible to detect the existence or prevent all of the cases of bombings and drug smuggling going on; however, it is possible to detect explosives and contraband substances in particular areas where high visibility and/or vulnerability exists such as in airports or airplanes. There are numerous ways in which an individual can place drugs or explosives on an airplane, and even more places an individual can hide the drugs or explosives once on the airplane. The illegal substances can be brought on the airplane by a knowing or unknowing individual by concealing the substance on his/her person or by placing the substances in baggage to be placed in the cargo section of the aircraft.
The methods for detecting substances such as explosives and drugs or narcotics have been studied for many years, and various techniques have been developed which range from explosives/drug sniffing dogs to highly sophisticated vapor detection devices. Basically, the detection of the aforementioned substances is accomplished in one of two ways; namely, non-vapor detection and vapor detection. Non-vapor detection methods include x-ray detection, gamma-ray detection, neutron activation detection and nuclear magnetic resonance detection. These methods of detection are more applicable to the detection of the various substances when the substances are concealed and are carried or associated with non-living items such as baggage to be carried onto an aircraft in that the detection techniques might pose a threat to living items. Vapor detection methods include electron capture detection, gas chromatography detection, mass spectroscopy detection, plasma chromatography detection, bio-sensor detection and laser photoacoustic detection. These methods of detection are more applicable to the detection of substances that are concealed and associated with living items such as those that can be carried by individuals including the residuals left on the individual who handled the various substances. All of the above methods are presently utilized, including explosive and drug sniffing dogs.
Today, there are many private and government research studies devoted to the development of systems and methods for the detection of explosives and drugs or narcotics. With the advances in explosives technology, such as the advent of the plastique explosives, which can be disguised as common items, it is becoming increasingly difficult to detect these substances. The problems that must be overcome in the detection of these substances as well as others, include low vapor pressure of the particular vapors escaping from the particular substance, the search time and the throughput of the various systems, the low concentration of vapor or particulate emissions from the particular substance, isolation of the particular substance with a high degree of reliability, and maintaining the integrity of the systems environment.
There is numerous prior art dealing with the technology of explosive and drug detection devices. The article "Air Flow Studies For Personnel Explosive Screening Portals" authored by R. L. Schellenbaum of Scandia National Labs which was published in 1987 as part of the Carnahan Conference on Securities Technology in Atlanta, Ga. (Jul. 15, 1987) discloses a study on various types of integrated systems for the detection of contraband explosives The study outlined a three step process, which includes the collection of vapor, preconcentration, and detection, for the capture and detection of the vapors emanating from explosive substances. The article discloses various types of collection devices for collecting the sample. Various portal configurations and air flow mechanics within each of the portals were studied to see which one provided the best sample. The Atmos-Tech Air Shower Portal, a Modified Atmos-Tech Portal and a Cylindrical Portal were used in the study with various air flow configurations. The study concluded that downward, semi-laminar flow over the body cross-sectional area combined with a vacuum flow collection funnel of approximately twelve inches in diameter placed beneath the grating in the floor of the portal was the best way to collect the explosives vapor or particulate emissions from an individual passing through the portal.
For the detection part of the study, various detection devices were used including the Phemto-Chem 100 Ion Mobility Spectrometer in combination with a preconcentrator developed by Ion Track Instruments Inc. The ion mobility spectrometer is a plasma chromatograph which uses an atmospheric ion-molecular reactor that produces charged molecules which can be analyzed by ion mobility. The preconcentrator comprises a motor-driven, metal screen disc rotated with a cast metal casing. The screen adsorbs the vapor and is then heated for desorption of the vapor. This adsorption-desorption process is the necessary preconcentration step which is used to increase the vapor and/or particulate concentration in the collected air sample.
The major problem encountered in the use of the portal detection systems in the study was maintaining the integrity of the sample air volume. In maintaining the integrity of the sample air volume, it is necessary to prevent the sample air volume to be contaminated with the ambient environment at the same time trying to maintain a steady flow of traffic through the portal, which is essential to efficient operation of any type of screening system in which heavy traffic is common place. The aforementioned article suggests that the integrity of the sample air volume was not maintained in portals without doors. If ambient drafts were present, such as those from air conditioners or just the flow of pedestrian traffic, a reduction of ten percent in detection was encountered. The addition of doors on the portals effected a rise in the detection rate; however, it produced unacceptable pedestrian traffic problems which would not meet the requirements for high throughputs required by airports.
In the patent art, there are a group of references which disclose various methods and devices for detecting contraband substances, including both drugs and explosives. These references are all directed to the detection of contraband substances within a container or luggage, and not those carried on a person. U.S. Pat. No. 4,580,440 and U.S. Pat. No. 4,718,268 both assigned to British Aerospace Public Company Limited disclose a method and apparatus for detecting contraband substances sealed in freight type cargo. Basically, the method consists of sealing the cargo in a container, agitating the cargo in order to shake off the vapor or particulate matter emanating from the cargo into the surrounding atmosphere, sampling the atmosphere, heating the collected sample and analyzing the sample utilizing gas chromatography. U.S. Pat. No. 4,202,200 assigned to Pye Limited discloses an apparatus for detecting explosive substances in closed containers. Basically, objects such as luggage are passed through a controlled axis tunnel wherein the objects are swept by circulating air flows, and then the air sample is collected and analyzed. It is also suggested that if a larger tunnel is constructed, people as well as objects can be passed through it. The aforementioned inventions provide a means and method for detecting contraband substances by using vapor sampling; however, none of the inventions provide or suggest the use of a preconcentrator means for increasing the sensitivity and selectivity of the detection means. Additional patent references which disclose similar type systems are U.S. Pat. No. 3,998,101 and U.S. Pat. No. 4,111,049.
There are numerous patent references in the testing and monitoring art which disclose a concentration step which includes the filtration or absorption of the molecules of interest over time. After a predetermined period of exposure, the filtering/absorption media is removed and desorbed with heat, while a new filter/absorption media is placed in the air stream. U.S. Pat. No. 3,768,302 assigned to Barringer Research Limited discloses a system used in the geological testing area and in which the system receives an air stream containing particulates. The sample undergoes a concentration step which includes passing the air sample over two paths with adsorbing/desorbing steps, and finally analyzed. U.S. Pat. No. 4,056,968 assigned to the same assignee as the above patent also discloses a system which is also used in the geological testing area. In this invention, the concentrated molecules could be desorbed from a moving tape as well as from a moving disk. U.S. Pat. No. 4,775,484 discloses a rotating filter media which is used to absorb particulate material during one stage of its rotation, and which is purged or cleaned at a separate and second stage of its rotation. U.S. Pat. No. 4,127,395 also discloses a common absorption/desorption circuit using a pair of absorbent media, wherein one of the pair is absorbing, while the other is desorbing. U.S. Pat. No. 3,925,022, U.S. Pat. No. 3,997,297 and U.S. Pat. No. 3,410,663 all disclose absorption/desorption type devices. All of the aforementioned devices disclose systems for the absorption and subsequent desorption of particulate or vapor matter; however, none disclose a portal type sampling chamber.